METHOD FOR SUPPLYING COOLING MEDIUM TO A GRINDING CUP AND GRINDING CUP TO CARRY OUT THE METHOD

Abstract: The present invention relates to a method for supplying cooling medium to a grinding cup (10; 10'; 10") for grinding buttons of a rock drilling bit. The invention also relates to a grinding cup (10; 10'; 10") to carry out the method. In prior art grinding cups the cooling medium is supplied via an axial boring extending through the entire grinding cup. This means that the cooling medium must also be guided through the grinding machine. The method according to the present invention supplies cooling medium to the portion of the grinding cup that is located axially between a recess (20) of a wear part (14) and the free end of a shank (12) of the grinding cup (10; 10'; 10"), said shank (12) being rotatably mounted in a grinding machine.

Description: METHOD FOR SUPPLYING COOLING MEDIUM TO A GRINDING CUP AND GRINDING CUP TO CARRY OUT THE METHOD Technical Field The present invention relates to a method for supplying cooling medium to a grinding cup for grinding buttons of a rock drilling bit, said grinding cup including a shank that is rotatably mounted in a grinding machine and a wear part having a recess, said recess carrying out the grinding of the buttons. The invention also relates to a grinding cup that is intended to be rotatably mounted in a grinding machine, said grinding cup carrying out grinding of buttons of a rock drilling bit, said grinding cup including a shank and a wear part, said wear part having a recess. Prior Art Background When grinding cemented carbide buttons of a drill bit, a grinding cup of the type described above is normally used. The wear part of such grinding cup usually has an abrasive grinding surface that often includes granular diamond. However, the grinding of cemented carbide buttons generates both heat and abrasive cuttings to such an extent that it is necessary to cool the grinding cup and the button bit as well as flushing away the cuttings. The known prior art technique for such cooling is to supply cooling medium, normally water, through the grinding machine and axially through the grinding cup to provide the cooling medium to be discharged in the region where the wear part of the grinding cup engages the free end of the button. This means that the cooling medium must be guided through the grinding machine to the rear end of the shank of the grinding cup and then axially through the shank of the grinding cup to the free end of the wear part. It is at once realized that the provision of means .for achieving such a cooling medium supply is a restriction from a designing point of view, i.e. when designing the grinding machine a lot of attention must be paid to the guiding of cooling medium through the grinding machine and consequently the machine becomes relatively seen complicated. Summary of the Invention The idea of the present invention is to present a method for supplying cooling medium to a grinding cup, said grinding cup being so designed that the cooling medium is not supplied via the rear end of the shank, i.e. via the grinding machine. Instead the cooling medium is supplied to the grinding cup without entering the grinding machine. The idea of the present invention is realized by a method for supplying cooling medium to a grinding cup and a grinding cup that has been given the characteristics of the appending claims. Description of Preferred Embodiments Below two embodiments of a grinding cup according to the present invention will be described, reference being made to the accompanying drawings, where Fig.l shows a partly sectioned side view of a first embodiment of the grinding cup according to the present invention; Fig.2 shows a partly sectioned side view of a second embodiment of the grinding cup according to the present invention; and Fig.3 shows a partly sectioned view of a third embodiment of the grinding cup according to the present invention. The grinding cup 10 according to Fig.l includes a shank 12, a wear part 14 and an intermediate portion 16 that bridges the shank 12 and the wear part 14. Preferably the shank 12 and the intermediate portion 16 are in one piece. The wear part 14 is connected to the intermediate portion 16 in a suitable way, preferably by brazing. However, within the present invention it is also possible that the wear part 14 is integral with the intermediate portion 16. The grinding cup 10 is symmetrical as of rotation relative to its longitudinal centre axis 18. The free end of the wear part 14 has a recess 20 in the shape of a segment of a sphere when the buttons have a hemispherical free end. However, if the buttons have ballistic or conical free ends then the recess of course has a complementary shape. Said recess 20 is intended to engage and cooperate with the free end of a button that is subjected to grinding. The button is preferably made out of cemented carbide and the recess 20 is equipped with an abrasive material, preferably diamond that can be in the shape of a matrix. If the wear part 14 is integral with the intermediate portion 16, i.e. the wear part blank is made out of steel, it can be suitable to electro-plate or in some other suitable way adhere a diamond layer to the wear part blank. In its upper part the intermediate portion 16 of the grinding cup 10 is provided with a key handle 19 that cooperates with driving means of the grinding machine to rotate the grinding cup 10. The intermediate portion 16 is further provided with a circumferential external groove 22 that has a certain extension in axial direction of the grinding cup 10. Preferably the depth of the external groove 22 is constant. A first hole 24, having radial direction, extends between the bottom of the external groove 22 and the region of the longitudinal centre axis 18. A second hole 26, having axial direction, extends between the area of the inner end of the first hole 24 and the bottom of the recess 20. The first and second holes 24, 26 communicate with each other in the area of their inner ends. In the circumferential external groove 22 a ring 28 of flexible material, e.g. plastic or rubber, is mounted. The height of the ring 28 is somewhat smaller than or essentially equal to the height of the groove 22. The inner periphery of the ring 28 is provided with a circumferential internal groove 30. In the area of contact between the bottom of the external groove 22 and the inner periphery of the ring 28, said ring 28 is provided with opposite tongues 32 that in active state perform a sealing action against the bottom of the external groove 22. In its mounted position the ring 28 covers the opening of the hole 24. The internal dimensions and tolerances of the groove 22 and the ring 28 must of course be adapted to each other in such a way that when the grinding cup 10 is rotated while the ring 28 is maintained stationary a proper sealing between the ring 28 and the groove 22 is carried out simultaneously as the friction between the ring 28 and the groove 22 is kept at a proper level. The ring 28 is also provided with a pipe 34 that extends in radial direction of the grinding cup 10. The pipe 34 extends through the wall of the ring 28, said pipe 34 being connected to the ring 28 preferably by vulcanization. The pipe 34 extends beyond the outer periphery of the ring 28 to a certain extent in order to be able to receive a hose 36, that is pushed onto the pipe 34. Preferably the pipe 34 is provided with a bulge 38 to achieve a better securing of the hose 36 on the pipe 34 . The described grinding cup 10 functions in the following way. The grinding cup 10 is mounted in the rotatable spindle of a grinding machine. The grinding cup is then adjusted in position relative to the button that is to be ground, i.e. a position where the wear part 14 engages the button. The grinding cup 10 is then rotated to perform grinding of the button. When the grinding cup 10 rotates the ring 28 remains stationary. Thus it is important that the dimensions and mutual tolerances of the groove 22 and the ring 28 are such that the intermediate portion easily 16 can rotate relative to the ring 28, the supply of cooling medium still being effected. Due to the flexibility of the ring 28 it is possible to mount the ring 28 in the groove 22 by pushing the ring 28 over the wear part 14 into the groove 22. The tongues 32 will deflect to allow such pushing of the ring 28 over the wear part 14. From an external source cooling medium is supplied to the recess 20 via the hose 36, the pipe 34, the groove 30, the first hole 24 and the second hole 26. When the space defined by the bottom of the groove 22 and the groove 30 is pressurized by the cooling medium then the tongues 30 of the ring 28 seal against the bottom of the groove 22 and simultaneously the side walls of the ring 28 are supported by the side walls of the groove 22. However, there is no definite requirement that this sealing is total. If there is a certain leakage of cooling medium between the tongues 30 of the ring 28 and the bottom of the groove 22, said cooling medium will flow downwards and cool the outside of the wear part 14. Such a cooling is normally favourable in a present grinding action. However, the dominating part of the cooling medium should be supplied via the holes 24 and 26. Preferably the length of life of the ring 28 is substantially the same as the length of life of the rest of the grinding cup 10. In the embodiment according to Fig.2 the grinding cup 10' includes a shank 12, a wear part 14 and an intermediate portion 16 that is integrally connected with both the shank 12 and the wear part 1 . The shank 12 is provided with a groove 13 that is intended to receive an O-ring that yieldably secures the shank 12 when mounted in the grinding machine. Preferably the shank 12 and the intermediate portion 16 are in one piece. The wear part 14 is connected to the intermediate portion 16 in a suitable way, preferably by brazing. However, within the present invention it is also possible that the wear part 14 is integral with the intermediate portion 16. The grinding cup 10' is symmetrical as of rotation relative to its longitudinal centre axis 18. The free end of the wear part 14 has a recess 20 in the shape of a segment of a sphere. As explained in connection with the embodiment according to Fig.l the shape of the recess can vary depending on the shape of the free end of the button. Said recess 20 is intended to engage and cooperate with the free end of a button that is subjected to grinding. The button is preferably made out of cemented carbide and the recess 20 is equipped with an abrasive material, preferably diamond that can be in the shape of a matrix, electro-plated to a steel body or in some other way adhered to the steel body. In its upper part the intermediate portion 16 of the grinding cup 10' is provided with a key handle 19 that cooperates with driving means of the grinding machine to rotate the grinding cup 10' . The intermediate portion 16 of the grinding cup 10' is further provided with a circumferential external flange 21 that separates the key handle 19 from a sub-portion 22 of the intermediate portion 16, the key handle 19 and the sub-portion 22 having different diameters. The sub- portion 22 having smaller diameter has a certain extension in axial direction of the grinding cup 10', said extension being defined by a circumferential slot 23. Preferably the external diameter of the sub-portion 22 is constant. A first hole 24, having radial direction, extends between the periphery of the sub- portion 22 and the region of the longitudinal centre axis 18. A second hole 26, having axial direction, extends between the area of the inner end of the first hole 24 and about halfway to the bottom of the recess 20. The first and second holes 24, 26 are connected with each other in the area of their inner ends. A third hole 27 extends from the region of the outer end of the second hole 26, said third hole 27 emanating in the recess 20. As can be seen in Fig.2 the third hole 27 is displaced in radial direction relative to the second hole 26 although the second and third holes 26, 27 are communicating with each other. This means that the third hole 27 will emanate eccentrically in the recess 20. In this connection it should be pointed out that the design and orientation of especially the third hole 27 can vary within the scope of the present invention. It is e.g. known prior art that the third hole emerges in the recess 20 via a slot having a length substantially equal to the diameter of the recess 20. In the circumferential sub-portion 22 a first washer 29, a ring 28 of flexible material, e.g. plastic or rubber, and a second washer 31 are mounted in consequtive order. The first washer 29 is in close contact with the flange 21. The total height of the first washer 29, the ring 28 and the second washer 31 is somewhat smaller than the axial extension of the sub-portion 22. In the slot 23 a locking ring 25 is mounted to secure the first washer 29, the ring 28 and the second washer 31 in axial direction. The inner periphery of the ring 28 is provided with a circumferential internal groove 30. In its mounted position the ring 28 covers the opening of the hole 24. It is important that the tolerances of the cooperating dimensions of the ring 28 and the sub-portion 22 are adapted to each other, i.e. the internal diameter of the ring 28 and the external diameter of the sub- portion 22. The sub-portion 22 must rotate relatively easy relative to the ring 28 and still there must be a proper sealing action between the ring 28 and the sub- portion 22 to guide cooling medium to the recess 20 via the holes 24,26,27. The ring 28 is also provided with a pipe 34 that extends in radial direction of the grinding cup 10' . The pipe 34 extends through the wall of the ring 28, said pipe 34 being connected to the ring 28 preferably by vulcanization. The pipe 34 extends beyond the outer periphery of the ring 28 to a certain extent in order to be able to receive a hose 36, that is pushed onto the pipe 34. Preferably the pipe 34 can be provided with a bulge to achieve a better securing of the hose 36 on the pipe 34. The grinding cup 10' according to Fig.2 functions principally in the same way as the grinding cup 10 according to Fig.l. However, the ring 28 is of slightly different design. When the space between the sub- portion 22 and the groove 30 is pressurized by cooling medium then the remaining portions 33 of the inner periphery of the ring 28 are urged apart in opposite directions to provide a sealing against the first and second washers 29, 31. The first washer 29 is in its turn urged against the flange 21 to provide a sealing against the cooling medium and the second washer 31 is urged against the locking ring 25 to provide a corresponding sealing. However, what has been said in connection with the embodiment according to Fig.l concerning leakage of cooling medium that cools the outside of the wear part 14 applies also for the embodiment according to Fig.2. The grinding cup 10" according to Fig.3 includes a shank 12, a wear part 14 and an intermediate portion 16 that bridges the shank 12 and the wear part 14. Preferably the shank 12 and the intermediate portion 16 are in one piece. The wear part 14 is connected to the intermediate portion 16 in a suitable way, preferably by brazing. However, within the present invention it is also possible that the wear part 14 is integral with the intermediate portion 16. The grinding cup 10" is symmetrical as of rotation relative to its longitudinal centre axis 18. The free end of the wear part 14 has a recess 20 in the shape of a segment of a sphere when the buttons have a hemispherical free end. However, if the buttons have ballistic or conical free ends then the recess of course has a complementary shape. Said recess 20 is intended to engage and cooperate with the free end of a button that is subjected to grinding. The button is preferably made out of cemented carbide and the recess Within the scope of the present invention it is also possible that there is no groove in the shank 12 but the ring 28 is locked axially by means of an O-ring that is pushed onto the shank 12. The ring 28 is also provided with a pipe 34 that extends in radial direction of the grinding cup 10. The pipe 34 extends through the wall of the ring 28, said pipe 34 being connected to the ring 28 preferably by vulcanization. The pipe 34 extends beyond the outer periphery of the ring 28 to a certain extent in order to be able to receive a hose 36, that is pushed onto the pipe 34. Preferably the pipe 34 is provided with a bulge 38 to achieve a better securing of the hose 36 on the pipe 34. The grinding cup 10" according to Fig.3 functions principally in the same way as the grinding cup 10 according to Fig.l. However, since the grinding cup 10" is not provided with a key handle the rotational driving of the grinding cup 10" is preferably carried out by having a chuck of the grinding machine to clamp the shank 12 to such an extent that rotational driving of the grinding cup 10" can be carried out. Within the scope of the present invention it is also possible to design the upper part of the shank 12 with a non- circular cross-section, e.g. a square cross-section, said cross-section engaging rotational driving means of the grinding machine. Since the ring 28 is of principally the same design for both embodiments the sealing by the tongues 32 is carried out in a correponding way. What has been said in connection with the embodiment according to Fig.l concerning leakage of cooling medium that cools the outside of the wear part 14 applies also for the embodiment according to Fig.3. Common for the described embodiments is that no axial boring through the shank need to be provided and also that the grinding machines will have an essentially simplified design since no cooling medium supply, e.g. in the shape of borings and sealings, through the grinding machine is necessary. This means that the degree of freedom when designing grinding machines is essentially increased.

Claims: AMENDED CLAIMS [received. by the International Bureau on 18 November 1994 (18.11. -94); original claims 1 and 4 amended; remaining claims unchanged (3 pages)] 1. Method for supplying cooling medium to a grinding cup (10;10';10") for grinding buttons of a rock drilling bit, said grinding cup (10;10';10") including a shank (12) that is rotatably mounted in a grinding machine and a wear part (14) having a recess (20) , said recess (20) carrying out the grinding of the buttons, c h a r a c t e r i z e d in that cooling medium is supplied to a portion (16; 12) of the grinding cup (10;10';10") that is located axially between the recess (20) and the free end of the shank (12) whereafter the cooling medium is supplied in an area where the wear part (14) engages the button and that the grinding cup is disposed of when it is used up. 2. Method according to claim 1 , c h a r a c t e r i z e d in that cooling medium is supplied to an intermediate portion (16) of the grinding cup (10;10') # said intermediate portion (16) being located axially between the shank (12) and the wear part (14) of the grinding cup (10;10') . 3. Method according to claim 1, c h a r a c t e r i z e d in that the cooling medium is supplied to the part of the shank (12) of the grinding cup (10") directed towards the wear part (14) . 4. Grinding cup (10; 10'; 10") that is intended to be mounted in a grinding machine, said grinding cup (10; 10'; 10") carrying out grinding of buttons of a rock drilling bit, said grinding cup (10;10';10") including a shank (12) and a wear part (14) , said wear part (14) having a recess (20) carrying out the grinding, c h a r a c t e r i z e d in that a portion (16; 12) of the grinding cup (10;10';10") located axially between the recess (20) and the free end of the shank (12) is provided with means (22,24,26,28,30,32,34; 21,22,23,24,25,26,27,28,29,30,31,33,-15,17,24,26,28,30, 32,34) for transferring cooling medium from an outside source to the recess (20) of the wear part (14) and that cooling medium is supplied in an area where the wear part (14) engages the button and that the grinding cup is disposed of when it is used up. 5. Grinding cup (10;10') according to claim 4, c h a r a c t e r i z e d in that the portion of the grinding cup (10;10') located axially between the recess (20) and the free end of the shank (12) is an intermediate portion (16) located between the shank (12) and the wear part (14) . 6. Grinding cup (10") accordning to claim 4, c h a r a c t e r i z e d in that the portion of the grinding cup (10") located axially between the recess (20) and the free end of the shank (12) is the part of the shank (12) directed towards the wear part (14) . 7. Grinding cup (10;10';10") according to any of claims 4-6, c h a r a c t e r i z e d in that the means for transferring cooling medium inludes a circumferential ring (28) of flexible material, the inner periphery of said ring (28) being provided with a circumferential internal groove (30) . 8. Grinding cup (10;10';10") according to any of claims 4-7, c h a r a c t e r i z e d in that the ring (28) is provided with means (34) for connection to a cooling medium source, said means (34) transferring cooling medium to the internal groove (30) of the ring (28) . 9. Grinding cup (10;10';10") according to any of claims 4-8, c h a r a c t e r i z e d in that the space provided between the ring (28) and the grinding cup (10;10' ;10") communicates with the recess (20) of the wear part (14) . 10. Grinding cup (10;10") according to any of claims 4-9, c h a r a c t e r i z e d in that the ring (28) includes two circumferential tongues (32) that contact an outer portion (22;12) of the grinding cup (10,-10") .

Inventors: BERGQUIST ARNE, BERGQUIST, ARNE
Applicants: SANDVIK AB
Application year: 1994
Main classification: B24B3
IPC codes: B24B3, B24B55, B24D7, E21B10